(1) Field of the Invention
The invention is related to a control system for controlling collective and cyclic pitch of rotor blades of a multi-blade rotor in a rotary-wing aircraft, said control system having a swash plate assembly and comprising the features of claim 1.
(2) Description of Related Art
A control system for controlling collective and cyclic pitch of rotor blades of a multi-blade rotor in a rotary-wing aircraft, in particular of rotor blades of a main rotor in a helicopter, is used in operation for rotating the rotor blades integrally around associated blade pitch control longitudinal axes by means of suitable pitch levers associated with the rotor blades that are operated by corresponding pitch control rods. Each pitch control rod is, therefore, connected to a rotating plate rotating in operation with and around a rotor axis of the rotor. This rotating plate is mounted to rotate on a non-rotating plate, which is restrained against any rotation around the rotor axis of the rotor by a connection connecting the non-rotating plate to a non-rotatable underlying structure of the rotary-wing aircraft, such as its fuselage or main gear box.
The rotating plate and the non-rotating plate define a so-called swash plate assembly and are usually annular and surround the rotor axis. This swash plate assembly is activatable by means of a suitable control input unit via associated control actuators for respectively controlling the collective pitch and the cyclic pitch of the rotor blades. More specifically, the swash plate assembly is adapted to transfer control inputs from a non-rotating system that includes the suitable control input unit and the non-rotating plate to a rotating system that includes the rotating plate and, when being mounted to the rotary-wing aircraft, also the rotor blades of the multi-blade rotor, i.e. the rotatable rotor as such.
In bigger rotary-wing aircrafts, the associated control actuators are frequently embodied by three servo-controlled jacks or similar actuators placed between the swash-plates and the non-rotatable underlying structure of the rotary-wing aircraft. These servo controlled jacks or similar actuators are respectively articulated by ball joints at their lower and upper ends on this non-rotatable underlying structure and in clevises of the non-rotating plate. Accordingly, spatial orientation of the non-rotating plate is controllable, wherein said non-rotating plate is adapted to entrain said rotating plate in tilting movements, i.e. for determining the spatial orientation of said rotating plate, which is connected to the pitch levers of the rotor blades by means of the pitch control rods. These pitch control rods extend between the rotating plate and the pitch levers and are respectively articulated by ball joints at their upper and lower ends on the pitch levers and in clevises that are distributed at the periphery of the rotating plate.
The rotating and non-rotating plates are usually displaceable axially parallel to the rotor axis for controlling collective pitch, and they can be tilted in any direction around the rotor axis for controlling cyclic pitch, by means of an axially displaceable central spherical bearing. The latter, on which the non-rotating plate is mounted in an oscillating manner, is generally centered on the rotor axis.
The document U.S. Pat. No. 3,508,841 A describes such a control system with a central spherical bearing on which a non-rotating plate of a swash plate assembly is mounted. The spherical bearing is mounted to a non-rotating sliding sleeve, wherein a rotor shaft of an associated rotor is rotatably received. This non-rotating sliding sleeve can be displaced axially parallel to a rotor axis of the rotor for controlling collective pitch, while rotating and non-rotating plates of this control system can be tilted in any direction around the rotor axis for controlling cyclic pitch.
In other known control systems, the spherical bearing is mounted axially displaceable parallel to the rotor axis around a cylindrical guide, which is arranged coaxially and non-rotatably to the rotor axis and generally fixed in relation to the non-rotatable underlying structure of the rotary-wing aircraft. When the rotating and non-rotating plates surround the rotor shaft, which is most often the case, the cylindrical guide is tubular, surrounds the rotor shaft and is rigidly fixed to a housing secured to the non-rotatable underlying structure of the rotary-wing aircraft.
The rotating plate is usually connected to the rotor by means of a suitable torque link in the form of one or more rotating arms, such that the latter entrain the rotating plate to rotation around the rotor axis in operation. The non-rotating plate, in turn, is non-rotatably connected as described above to the non-rotatable underlying structure of the rotary-wing aircraft by means of a suitable stop arm that inhibits relative rotational movement between the non-rotating plate and the non-rotatable underlying structure of the rotary-wing aircraft.
The document U.S. Pat. No. 5,599,167 A describes such a control system with a rotating plate that is driven in rotation by a rotor shaft of an associated main rotor with the aid of one or more torque links that are embodied as so-called rotating scissors fittings, which are articulated by one end to the rotor shaft and by the other end to the rotating plate. The latter is additionally mounted so that it can rotate, with the aid of a ball-bearing, coaxially on a non-rotating plate that can be tilted in any direction around a rotor axis of the rotor shaft, while being mounted to a central spherical bearing. This central spherical bearing can be displaced parallel to the rotor axis by an axial sliding of the central spherical bearing about a cylindrical tubular guide, which cannot rotate as it is non-rotatably fixed to stationary points of a non-rotatable underlying structure. The non-rotating plate of the control system is held back against any rotation about the rotor axis by a so-called non-rotating scissors fitting, which is articulated by one end to the non-rotating plate and by the other to the base of the cylindrical tubular guide.
The document U.S. Pat. No. 6,033,182 A also describes such a control system with a rotating plate. However, the latter is connected to an associated rotor by means of two torque links, which are embodied as scissor-articulated rotating arms, each having an upper and a lower arm that are pivot hinged onto each other, the lower arm being connected by a ball joint onto the rotating plate and the upper arm being pivotably mounted to a clevis of a torque link driver provided on a rotor shaft of the associated rotor. The non-rotating plate of the control system is non-rotatably connected to a non-rotatable underlying structure by means of a suitable stop arm, which is embodied as a rigid arm that is fixed on an external radial support provided integrally with a conical housing that is non-rotatably attached to the non-rotatable underlying structure. The stop arm is integral with the non-rotatable underlying structure and comprises an axial arm part with a “U” shaped transverse section delimiting a groove that forms a rigid rotation stop track of a stop pin that is integral with the non-rotating plate.
However, the stop arms of the above described control systems must be configured comparatively long in order to allow connection of the non-rotating plate to the non-rotatable underlying structure of the rotary-wing aircraft. This comparatively long configuration requires a comparatively high rigidity of the stop arms and, consequently, a comparatively heavy weight. Another disadvantage consists in a resulting aerodynamic drag in operation, which is naturally higher when using such large stop arms.
While the control systems of bigger rotary-wing aircrafts frequently use spherical bearings as described above, control systems of some smaller and mid-size rotary-wing aircrafts use gimbals with e.g. cardan-joint or u-joint rings for mounting at least a non-rotating plate of a swash plate assembly of the control system in an oscillating manner. The gimbals can be mounted on associated sliding sleeves, which are glidingly arranged on cylindrical tubular guides that surround rotor shafts of associated rotors.
In such control systems, corresponding control inputs to the swash plate assembly can be mixed by a control input unit that is embodied e.g. as a so-called mixing lever gear unit and arranged underneath the swash plate assembly. For collective pitch control, the sliding sleeve can be displaced axially parallel to a rotor axis of the associated rotor by a mixing lever gear unit fork of the mixing lever gear unit. In this case, a stop arm or scissor between the non-rotating plate of the control system and a non-rotatable underlying structure of the rotary-wing aircraft is not required, as the non-rotating plate can be rigidly fixed by the gimbal ring to the sliding sleeve, which, in turn, is conjoined with the mixing lever gear unit fork.
The document U.S. Pat. No. 7,037,072 B2 describes a control system with a central gimbal that is centered on a rotor axis of a rotor shaft of an associated rotor. The central gimbal, on which the rotating and non-rotating plates of an associated swash plate assembly are mounted in an oscillating manner, is rigidly fixed, i.e. in an axially immobile manner, to a collar, which is arranged coaxially to the rotor axis and rigidly and non-rotatably attached to a non-rotatable underlying structure.